Radioactivity

Radioactivity

1. ?

   • When an atom has an unstable nucleus
     • It emitts radiation to become stable, this is a random process
   • Isotope
   • DANGER

2. Background Radiation

   • Natural
     • Rocks
     • Cosmic Rays
   • Manmade
     • Weapons Tests
     • Radioactive Power Stations
     • Nuclear Accidents

3. Investigating Atoms

   • Plum Pudding
     • 100 years ago
     • Sphere of positive charge with negative elctrons spread through
   • Rutherford
     • Scattering Technique
     • Fired alpha particle at thin foil
       • Some went through, some bounced back
       • Conclusion= atom is small central nucleus surrounded by electrons orbiting in shells

4. Types of Radiation

   • Alpha
     • Emitts two protons and two neutrons
     • Emitts helium nucleus
     • Stopped by air/paper
     • Travels a few cm
     • Deflected away from positive; deflected a lot because its large
   • Beta
     • Emitts high speed electron
     • Travels a few m
     • Stopped by thin aluminium
     • Deflected away from negative; deflected less because its small
   • Gamma
     • Wave
     • Travels many m
     • Stopped by thick lead or concrete
     • Not deflected because no charge

5. Uses of radioactivity

   • Carbon Dating
     • Find age trees
     • Living wood contains radioactive carbon (half-life=5600 years)
     • Compare count rate from sample to that of living wood
   • Uranium dating
     • Find age igneous rocks
     • Uranium decays into lead
     • Measure amount of lead and uranium in sample
   • Sterilising medical equipment
   • Destroy Cancerous cells
   • Radioactive tracers
     • Trace flow of substance through system
     • Drink radioactive substance
       • Detectors placed on each kidney
         • Detector up and down= normal kidney (substance flows in and out)
         • Detectors stays up= blocked kidney (substance can't come back out)
     • Iodine used
       • Half life= 8 weeks
         • Long enough for test but decays quickly
       • Emitts gamma which can be detected outside body
       • Decays into stable product
   • Automatic Thickness Monitoring
     • Make foil
     • Amount of beta radiation passing through foil depends on its thickness
     • If thickness increases too much, detector sends signal to rollers to increase pressure